The present invention relates to a soil conditioning composition and a method of using same, and more particularly to an improved soil conditioning composition having an extended useful life in soil.
The use of organic mulches to create a protective covering over soil, thereby to reduce the evaporation loss of moisture from the soil, is well known. Typical of these organic mulches are loose, chopped, pulverized or shredded organic materials such as wood chips, hay, grass clippings or sawdust. More recently "plastic mulches" have been used, these being several mil thick sheets of plastic (for example, high molecular weight polyethylene) which are placed over the soil for the same purpose. Typically the plastic mulches are provided with apertures allowing for the planting of crops from above and the penetration of growing crops from below. An alternative to the use of the organic and plastic mulches which are placed on top of the soil has been the use of "super-slurper" polymers. These are usually water-insoluble, cross-linked, hydrophilic polymers that swell when in contact with water to absorb 10 to 30 times their weight in moisture. The water-insoluble polymers are placed in the soil and retain large amounts of soil water without influencing the physical properties of the water or the soil-water/soil-matrix interaction.
An alternative to use of the above-mentioned mulches has been the use of water-soluble polymers placed in the soil. When placed within the soil environment, these water-soluble materials dramatically alter the flow of moisture through the soil and increase water retention. Among the water-soluble polymers utilized for this purpose are high molecular weight poly (ethylene oxide), polyvinyl alcohol, polyvinyl pyrrolidone and polyacrylamide (whether hydrolyzed or not). The use of these polymers is suggested in such patents as U.S. Pat. Nos. 3,633,310; 3,798,838; 3,909,228; and Japanese Pat. No. 47-2528 (1972). It will be appreciated that these linear, water-soluble, hydrophilic polymer mulches directly control the physical properties of the soil water by modifying its viscosity, surface tension, and contact angle, and hence act in an entirely different manner than the cross-linked, water insoluble, hydrophilic "super-slurper" polymers or polymers used to aggregate soil particles. They are particularly useful in increasing the retention of water by coarse-textured soils through reducing evaporated and deep percolation.
The linear, water-soluble polymers have not proven to be entirely satisfactory in use as the residence time of these polymers tends to be very short when applied to natural soils and under the conditions prevalent in a natural environment. Despite their functional attractiveness, the tendency of these polymers to washout (that is, be removed from their area of utility within the soil) has made them economically unattractive as they must be constantly replaced in order to maintain them at the desired functional level.
Accordingly, it is an object of the present invention to provide a soil conditioning composition composed of a linear, water-soluble, hydrophilic polymer characterized by a low washout rate from soil.
It is another object to provide such a composition which will remain in the soil for a long period of time, thereby rendering the composition more cost-effective.
A further object is to provide a method of irrigation utilizing such a composition.